The present invention relates to optical fiber connectors for connecting optical fibers in a variety of optical communication apparatuses, and more precisely to a method for polishing the end faces of ferrules for axially supporting optical fibers in optical fiber connectors, and to a machine for polishing the end faces of such ferrules.
Presently, optical fibers are used as transmission lines in the field of telecommunication to increase transmission capacity. It is known that optical fibers may be joined by fusion splicing wherein the end faces of the optical fibers are permanently connected by adhesion or welding, or by use of a disconnectable optical fiber connector. When optical connectors are used, axial deviation of the fibers must be held to less than 1/10 of their diameters and good contact between the end faces of the fibers is required. In order to meet such requirements, end face contact type optical connectors are often used. In such connectors, a ferrule is attached to the end portion of each optical fiber, and the ferrules at the fiber ends to be connected are respectively inserted from opposite ends of a sleeve. The end faces of the ferrules are butted against each other, and the ferrules are fixed in position by tightening the sleeve using a coupling nut.
FIG. 1 illustrates an optical fiber having one of its ends attached to a ferrule to be connected in a connector. In FIG. 1, the reference numeral 1 denotes an optical fiber, and the numeral 2 designates a secondary coated optical fiber formed by covering the circumference of an optical fiber 1 with a coating material such as nylon, etc. The circumference of secondary coated optical fiber 2 is braided with high tensile strength tension members 4, and members 4 are covered with a coating of polyvinylchloride (PVC) etc. to form an optical cable 3. A cylindrical ferrule 5 has a chip 6 and one of its end, and an axial capillary centered with high accuracy extends through chip 6. The outer coating and the tension members 4 are cut away from cable 3 at one end to expose the secondary coated optical fiber 2, and the latter is also cut away at a position near the end face of the connecting point to expose a length of fiber 1. The exposed length of optical fiber 1 is inserted into the center capillary of chip 6 as shown in FIG. 1. The exposed secondary coated optical fiber 2 is inserted into the ferrule and is fixed therein, using, for example, an epoxy resin adhesive. The end faces of optical fibers to the connected are polished together with their respective ferrules, and the same are coaxially aligned by insertion into a common sleeve. Ferrule 5 may be provided with a flange 7, as shown in FIG. 1, and such flange may be used for manipulating and positioning ferrule 5.
In optical fiber connectors of the type described, connection losses are greatly influenced by the accuracy of the cutting of the end faces of the ferrules. For example, as shown in FIG. 2, due to mechanical inaccuracies of polishing machines, end faces 5a of ferrules 5 are often polished so that the faces 5a are inclined at an angle .alpha. relative to the plane extending at right angles to the longitudinal axis of the ferrules 5.
With reference to FIG. 3, it can be seen that when a ferrule 5 having an incorrectly polished end face 5a is inserted into a sleeve 8 and is abutted against the end face 5'a of another ferrule 5', a gap G is formed between the end faces of the optical fibers 1 and 1'. In practice, such gap G is apt to vary in many ways due to backlash of the polisher. This causes a multi-reflection situation and interference in the transmission of light between the end surfaces of the optical fibers 1 and 1', resulting in increased and fluctuating connection losses. Therefore, stable and effective connections are difficult to achieve. On the other hand, if the gap G is very large, in the order of 8-10 .mu.m or more, for example, fluctuations in connection loss are reduced, but the connection loss itself is increased.